Waterproofing membranes having flexible plastic sheets for carrying a preformed, pressure-sensitive adhesive layer have been used for a number of years to provide protection to existing building surfaces. The adhesive layers are typically made of rubber-modified bitumen, which is aggressively sticky, and is covered by a release sheet that is removed before attaching the membrane to the substrate surface.
A technique for “reverse tanking” waterproofing is described in U.S. Pat. No. 4,994,328 of Cogliano (bituminous adhesive) and U.S. Pat. No. 5,316,848 of Bartlett et al. (non-bituminous synthetic adhesive). According to this technique, the waterproofing membrane is first attached with the back side of its carrier sheet against a “formwork” (i.e., concrete mold usually formed by wooden boards joined together). Consequently, the waterproofing adhesive layer faces outwards. A concrete structure is created by casting concrete against the membrane-covered formwork surface, and this may be referred to as “post cast” or “post applied” concrete. The adhesive layer is covered by an elastomeric protective coating layer, a particle coating layer, or mixture or arrangement of both (i.e., either individually, mixed together as one layer, or arranged as discrete layers), to protect the adhesive from dirt and damage. This protective coating layer (whether of polymeric or particle coating) also operates to decrease the tack of the adhesive. The outer surface is further protected by a release sheet liner (that must be removed before fresh concrete is poured against the adhesive/protective coating layers). After curing, the concrete is bonded with the adhesive/protective coating layers, and thus a waterproofing bond is achieved in “reverse” order.
Hence, in the world of “reverse tanking” waterproofing, it can be said that the waterproofing is “pre-applied” because it precedes the concrete structure; and, in turn, the concrete is said to be “post cast” or “post applied” because it follows installation of waterproofing.
Reverse tanking is further discussed in U.S. Pat. Nos. 5,496,615 and 6,500,520 which teach using particle coating layers. In the '615 patent, inorganic particles are used to resist foot traffic when the membrane is installed on a horizontal surface. In the '520 patent, particles are applied on top of an adhesive layer to enhance bonding with concrete by reacting with calcium hydroxide generated during hydration of cement.
One of the difficulties of reverse tanking is achieving continuity of waterproofing in detail areas (i.e., surface irregularities), and especially in “tieback” detailing. Tiebacks are the terminal ends of rods or cables supporting the formwork and found protruding at intervals through the formwork surface. Other surface irregularities include penetration areas, such as where pipes or pile caps extend through the formwork.
FIG. 1 illustrates the present process used in the industry for waterproofing “tiebacks” on concrete formworks. Drainage mats or sheets, which usually involve a fabric attached to a cuspated core sheet, are placed against the wooden formwork, and covered by sheets of reverse tanking waterproofing membrane, previously described above. Such sheet materials are available from Grace Construction Products, Cambridge, Mass., under the trademarks HYDRODUCT® (drainage) and PREPRUFE® (waterproofing membranes). These sheet materials are required to be cut and arranged to surround the area on the formwork occupied by the tieback, which can be as large as a man's chest.
As shown in FIG. 1, a wooden or metal box must be fabricated and fitted over the tieback. The box is fastened to the formwork, such as by screws and brackets, with a bead of adhesive for sealing around the edges against the formwork. The box is filled with liquid mastic or mortar cement to prevent twisting or collapse of the box due to the poured concrete.
As shown in FIG. 2, the box is covered with waterproofing strips. The strips are available as a double-sided adhesive “tape” from Grace Construction Products under the PREPRUFE® brand name. One side has a tacky adhesive that sticks onto the box and surrounding formwork; the other side has a coated adhesive layer for bonding to post cast concrete. Although FIGS. 1 and 2 illustrate a finished tape “box” shape, the actual waterproofing of the box with strips requires painstaking labor. The tape strips must be overlapped to provide a continuous barrier over and around the tieback. Fabricating, fastening, and waterproofing each box at a tie back detail requires about 30 minutes or more. In formwork installations that exceed one thousand square feet, one may confront one hundred tiebacks. Providing waterproofing for such detail areas as these would thus require days of labor.
In view of the foregoing disadvantages, a novel method and waterproofing membrane system are needed for decreasing labor costs in waterproofing installations wherein tiebacks, pipe penetrations, pile cap penetrations, and other surface irregularities are encountered.